1. Field of the Invention
The present invention relates to a machine for cleaning ballast supporting a track, which comprises a machine frame supported on undercarriages running on the track and carrying a ballast screening arrangement, a ballast excavating device including a revolvable excavating chain arranged to deliver excavated ballast to the screening arrangement for cleaning the excavated ballast, and a conveyor arrangement disposed to receive the cleaned ballast from the screening arrangement and to discharge the cleaned ballast for support of the track.
2. Description of the Prior Art
A variety of such ballast cleaning machines are well known. U.S. patent application Ser. No. 08/036,712, filed Mar. 25, 1993, now U.S. Pat. No. 5,394,944, for example, discloses a track-bound ballast cleaning machine with an elongated machine frame which carries a vertically adjustable ballast excavating device. This device includes an endless excavating chain comprising a transversely extending strand which moves during operation underneath the track, excavates ballast and conveys it to a screening arrangement. The screening arrangement separates the detritus from the excavated ballast and conveys it to a forward end of the machine while the cleaned ballast is deposited by a conveyor arrangement underneath the track for support thereof. Instead and/or additionally, more clean ballast or other track bed bulk material may be conveyed from the rear end of the machine and may be discharged on the exposed sub-grade. At the beginning of the operation of such known ballast cleaning machines, a gap must be excavated in the ballast bed to enable the transversely extending excavating chain strand to be introduced underneath the track.
German patent No. 2,226,612 discloses a ballast cleaning machine which comprises a respective excavating device at each side of the machine frame and track rail. Each excavating device comprises a beam about which an endless excavating chain revolves, and each beam is rotatable about a vertical axis extending at one end of the beam and is vertically adjustable. For excavating ballast under the track, the beams are lowered onto the track shoulders and are rotated inwardly to extend below the track. Upon revolution of the excavating chains, the ballast is excavated and conveyed to the track shoulders where upwardly inclined bucket elevators convey the excavated ballast to a screening arrangement for cleaning.
It is also known to remove ballast from a track bed by suction. Such a machine has been disclosed in British patent No. 2,172,326. This machine comprises three suction pipes spaced from each other in a transverse direction to aspire ballast from the two shoulders and the center of the ballast bed. Rotatable scarifying tools are attached to the suction pipe ends having the suction openings to scarify encrusted ballast before it is aspired. The cleaned ballast is returned to the track.
Other machines using suction for removing ballast from a track have been disclosed in German patent No. 2,136,306 and German utility model No. G 8,236,650.0.